1. Field of the Invention
The invention relates to a hydraulic control apparatus and a hydraulic control method that are used to control a hydraulic pressure that is supplied to a low hydraulic pressure supplied portion and a hydraulic pressure that is supplied to a high hydraulic pressure supplied portion.
2. Description of the Related Art
Japanese Patent Application Publication No. 03-134368 (JP-A-03-134368) describes an example of an apparatus that supplies hydraulic pressures to a low hydraulic pressure supplied portion and a high hydraulic pressure supplied portion. According to the JP-A-03-134368, a high pressure oil pump is used to supply a hydraulic pressure to a pulley of a V-belt continuously variable transmission that requires a high hydraulic pressure, and a low pressure oil pump is used to supply a hydraulic fluid to a hydraulic clutch and a hydraulic power transmission that require a hydraulic fluid that has a relatively low hydraulic pressure but a high flow volume.
Japanese Patent Application Publication No. 2006-226351 (JP-A-2006-226351) describes a hydraulic control apparatus. With this hydraulic control apparatus, in the case where different magnitudes of hydraulic pressures are supplied from single electrical oil pump, a load of the electrical oil pump is smoothly changed. Especially, when a circuit to which the electrical oil pump is connected is changed from a low pressure hydraulic circuit to a high pressure hydraulic circuit, the circuits are changed after the rotational speed of the electrical oil pump is decreased to a value equal to or lower than a predetermined value. Japanese Patent Application Publication No. 2000-45807 (JP-A-2000-45807) describes an apparatus that executes a vehicle engine stop control. With this apparatus, when an engine is automatically stopped, an electrical hydraulic pump supplies oil to an automatic transmission. If the electrical hydraulic pump malfunctions, the engine is not automatically stopped. Japanese Patent Application Publication No. 2007-145050 (JP-A-2007-145050) describes a drive system for a vehicle that is able to travel using drive power generated by a motor. With this system, if a mechanical hydraulic pump and an electrical hydraulic pump, which supply hydraulic pressures to a hydraulic circuit for a transmission, malfunction and a required hydraulic pressure is not achieved, the torque that is output from the motor is limited.
According to JP-A-03-134368, because two types of oils pumps, that is, the low pressure oil pump and the high pressure oil pump, are provided, it is possible to supply the hydraulic pressures that are required by a torque converter, a clutch and the continuously variable transmission. As a result, the torque that is required to drive the oil pumps is reduced as a whole, and power loss and hydraulic pressure shortage are prevented or suppressed. However, with the configuration described in JP-A-03-134368, the oil pump that supplies a hydraulic pressure to the portion that requires a high hydraulic pressure and the oil pump that supplies a hydraulic pressure to the portion that requires a relatively low hydraulic pressure operate independently from each other. Therefore, if the high pressure oil pump malfunctions, a high hydraulic pressure is not supplied.
According to JP-A-2006-226351, changing the operating state of the electrical oil pump makes it possible to supply hydraulic pressures within a hydraulic pressure range from a relatively low hydraulic pressure to a relatively high hydraulic pressure. Therefore, if the electrical oil pump malfunctions, a required hydraulic pressure may not be supplied and power loss of the electrical oil pump may increase. In the control apparatus described in JP-A-2000-45807, the electrical oil pump is provided to avoid the situation where the hydraulic pressure goes away when the engine is restarted. Therefore, if the electrical oil pump malfunctions, the hydraulic pressure goes away. In addition, according to JP-A-2007-145050, if both the mechanical hydraulic pump and the electrical hydraulic pump malfunction and a sufficient hydraulic pressure that needs to be supplied to the transmission is not achieved, the torque that is output from the motor is limited. Therefore, it is possible to suppress damage to the transmission due to hydraulic pressure shortage. However, with the configuration described in JP-A-2007-145050, the torque that is output from the motor is limited to the minimum torque at which damage is not given to the transmission. Therefore, the drive torque corresponding to a requested travel motion may not be achieved.